EXTERNAL CHARACTERS AND HABITS 69
which more or less complete!}" surrounds the face in many species. The nose is flat, but well-marked, and the ears are more or less concealed in thick fur. The upper lip is short, and both lips are bulged forwards by the prognathous jaws. The eyes are bright, and the eyelashes are poorly developed. The neck is short.
The whole body has a thick covering of hair, but the hairs on the face are scanty. The colour varies at different ages, being fulvous or greyish in the first three years of life, but darker after that.
Pocock (223) points out that there is a considerable individual variation in the colour, and he states that the hue in a Hainan Gibbon altered concomitantly with the onset of menstruation. The skin is black. There are two pectoral mammae.
ffabits.*—The Gibbons are gentle, affectionate creatures, but there is evidence that they bite severely when they are irritated. They are also very timid, and the sight of an enemy makes them take refuge in flight.
Their vocal powers are considerable, and their penetrating cries are audible for miles. Dr. Salomon Muller, an observant and careful naturalist, in describing the voice of the Siamang said (87), " the voice is grave and penetrating, resembling the sounds gnek, goek, gtiek, goek, goek, ha ha ha ha haaaaaa, and may easily be heard at a distance of half a league/' Martin (355) described the cry of the agile Gibbon as " overpowering and deafening in a room, and from its strength, well calculated for resounding through the vast forests." Pocock (223) contrasted the voices of the Hainan and
* Accounts of the habits are contained in papers 176, 180, 182,
2IO, 215, 223.